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H.S. Bridge, scientist who mapped solar winds, dies at 76

A memorial service for Professor Emeritus Herbert S. Bridge will be held in the MIT Chapel at 1:30pm on Thursday, Sept. 14.

Dr. Bridge, professor emeritus of physics and an internationally known space scientist who played a key role in mapping the solar winds that flow through interplanetary space, died August 30 at Massachusetts General Hospital after a long illness. Dr. Bridge, who lived in Sudbury, was 76. The family said the cause of death was coronary artery disease.

As associate director and later director of the MIT Center for Space Research, Professor Bridge was one of the pioneers in the exploration of the solar system from unmanned spacecraft.

He was the leader of a group of physicists at MIT who designed and constructed a novel instrument for the study of interplanetary plasma, the modulated-grid Faraday cup. This instrument, successfully flown aboard Explorer X in the spring of 1961, for the first time provided direct evidence for the existence of a dilute plasma in interplanetary space (the supersonically expanding outer atmosphere of the sun), as well as supplying some preliminary information of the density and velocity of this plasma.

After that initial discovery, Professor Bridge was principal investigator on space plasma experiments aboard unmanned scientific missions to every planet in the solar system with the exception of Pluto.

The pioneering work of Professor Bridge and his collaborators received worldwide recognition and the MIT group acquired a leading position in the field of plasma measurements in outer space. Plasma probes have been successfully flown on seven NASA earth satellites, two deep space probes and four planetary missions.

These experiments have provided a wealth of accurate data on the properties of the interplanetary plasma, on the earth's magnetosphere, and on the interaction of the solar wind with the Moon, Venus and Mercury, Mars, Jupiter, Saturn, Uranus and Neptune.

Professor Bridge's plasma experiment on board the Voyager spacecraft directly measured the properties of plasmas originating from the volcanoes on Io (the innermost Galilean satellite of Jupiter), from the dense atmosphere of Titan (the large satellite of Saturn), from the upper atmosphere of Uranus, and from Triton (the large satellite of Neptune). Ultimately, his experiment on the Voyager spacecraft may measure the plasma in the interstellar medium. The Voyager spacecraft are currently at about 50 Astronomical Units from the Sun, and continue to measure the properties of the distant solar wind.

Professor Bridge obtained his bachelor's degree from the University of Maryland in 1941. During the war, he was a member of the staff of the National Defense Research Council Separation Project at Princeton and then a member of the staff of the Los Alamos Laboratories.

In 1946 he came to MIT, where he received his PhD in 1950. From 1950 until 1966 he was a member of the research staff of MIT's Laboratory for Nuclear Science. During 1957, he took a leave of absence from MIT to work at the CERN Laboratory at Geneva, Switzerland. He did work on high-energy particles at CERN and at Brookhaven National Laboratory. He was appointed professor of physics at MIT in 1966.

His early work in cosmic rays was mainly directed toward the study of nuclear interactions produced by cosmic ray particles and of the new unstable particles resulting from these interactions.

Professor Bridge was associate director of the MIT Center for Space Research from its inception in 1965 until 1978. He was appointed director in 1978 and served until 1984, when he retired and became professor emeritus.

Professor Bridge also contributed effectively to MIT's educational program through formal teaching and, more importantly, the training that graduate students and young PhDs received under his leadership.

He was a member of the American Geophysical Society, a Fellow of the American Geophysical Union and the American Academy of Arts and Sciences, and a member of Phi Beta Kappa. He was awarded the NASA Medal for Exceptional Scientific Achievement in 1974.

In addition to his professional accomplishments, Professor Bridge had a number of outside interests, including cars, photography, mountaineering and the out-of-doors. His combined interests in high-energy particles and mountaineering took him to high-altitude laboratories throughout the world.

He is survived by his wife, Jeanne of Sudbury; three children, Raymond Bridge of Boulder, CO, Clare Bridge of York, MT, and Bill Bridge of Thetford, VT; four grandchildren; and two brothers, James of Los Alamos, NM and Richard of Silver Spring, MD.

A version of this article appeared in MIT Tech Talk on September 13, 1995.

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